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Pressure-sensitive paint (PSP) was applied to the surface of a NACA0012 airfoil to investigate pressure fluctuations associated with trailing edge (TE) noise under low-velocity flow conditions. The primary focus is to assess the feasibility of employing laser pulses exposed at the airfoil surface to mitigate TE noise. However, the weak pressure fluctuations accompanying TE noise pose a challenge, as they are overshadowed by image sensor noise in high-speed cameras capturing PSP emission changes. To address this issue, a novel time-resolved phase-locking technique was introduced, utilizing the signal from a semiconductor pressure transducer at the trailing edge as a phase-lock trigger source. By repetitively conducting phase-locked measurements (1150 times), time series ensemble averaged data based on PSP emission images were obtained, enabling the capture of these subtle pressure fluctuations. Quantitatively, fluctuations with a dominant frequency of 679 Hz and an amplitude of 50 Pa are resolved within an accuracy of about 15 Pa, achieved at a recording rate of 19.2 kHz. Both the suppression and subsequent redevelopment of the pressure field with the TE noise offer valuable insights into the dynamics of TE noise and open avenues for targeted noise reduction strategies in aerodynamic applications. [ABSTRACT FROM AUTHOR]

Combined measurement of shape and aerodynamic force is effective for understanding the mechanism of transonic wing flutter. To explore one method, a random-dot pressure-sensitive paint (PSP) was applied to the time-resolved global measurement of the deformation and pressure field of a transonic flow over an airfoil. The random-dot PSP has a patterned texture with luminescence intensity, which is made by intentional photodegradation of a PSP dye. These dots allow simultaneous measurement of pressure and the surface profile of the airfoil using stereo-digital image correlation. The feasibility of the random-dot PSP was tested in a transonic wind tunnel using a three-dimensional backswept wing model, which started to flutter at Mach 0.89 with a dominant frequency of 100 Hz. The unsteady surface profile and pressure distribution of the airfoil were measured using 12-bit high-speed cameras as the deformation amplitude increased. The experimental results indicate that the deformation and surface pressure distribution during flutter were successfully measured over time. The accuracy of the measured deformations and pressures was evaluated by comparison with several point data obtained with a laser displacement meter and semiconductor pressure transducers. The accuracy at each time-resolved image obtained at a recording rate of 6.25 kHz was within 1 mm for displacement and about 1 kPa for pressure. [ABSTRACT FROM AUTHOR]

Time-series data, such as unsteady pressure-sensitive paint (PSP) measurement data, may contain a significant amount of random noise. Thus, in this study, we investigated a noise-reduction method that combines multivariate singular spectrum analysis (MSSA) with low-dimensional data representation. MSSA is a state-space reconstruction technique that utilizes time-delay embedding, and the low-dimensional representation is achieved by projecting data onto the singular value decomposition (SVD) basis. The noise-reduction performance of the proposed method for unsteady PSP data, i.e., the projected MSSA, is compared with that of the truncated SVD method, one of the most employed noise-reduction methods. The result shows that the projected MSSA exhibits better performance in reducing random noise than the truncated SVD method. Additionally, in contrast to that of the truncated SVD method, the performance of the projected MSSA is less sensitive to the truncation rank. The projected MSSA achieves denoising effectively by extracting smooth trajectories in a state space from noisy input data. Expectedly, the projected MSSA will be effective for reducing random noise in not only PSP measurement data, but also various high-dimensional time-series data. [ABSTRACT FROM AUTHOR]

The transonic buffet on an ONERA-M4 model was experimentally investigated using an unsteady pressure-sensitive paint (PSP) in the present study. Wind tunnel tests were conducted in a blowdown-type transonic wind tunnel at a Mach number of 0.84 and a chord Reynolds number of 2.0 × 10 6 . The angle of attack was varied in between - 3. 0 ∘ and 4. 0 ∘ . The left wing was painted with a polymer/ceramic PSP with low surface roughness, and the right wing was painted with a temperature-sensitive paint. The measured PSP data were processed to calculate time-series pressure coefficients, root-mean-squares pressure-coefficient fluctuations, power spectral density, coherence, and phase shift. The behavior of the unsteady pressure field was different from that observed for the NASA Common Research Model (CRM) in a previous study. The dominant frequency of the shock oscillation shifted from the low-Strouhal-number component ( S t < 0.05 ) to the bump Strouhal number ( S t = 0.11 for the center frequency) with increasing angle of attack. The separation processes with an increasing angle of attack were also found to be different for the two models. The separation starts from the mid-span region in the CRM, while the separation starts from the wingtip in the ONERA-M4 model. The characteristic pressure fluctuations known as "buffet cells" were not observed for the ONERA-M4 model. These differences are considered to be caused by the difference in model geometries, such as the wing twist and the airfoil cross-sectional profile. [ABSTRACT FROM AUTHOR]

Unsteady pressure fields on a civil aircraft wing near the onset of transonic buffet have been investigated experimentally to identify flow unsteadiness that relates to the buffet onset determined by global criteria. An 80%-scale NASA Common Research Model was tested in the JAXA 2 m × 2 m Transonic Wind Tunnel at a Mach number of 0.85 and a chord Reynolds number of 2.27 × 106. The angle of attack was varied in small increments around the buffet onset angle determined by global criteria based on the lift curve and wing-root strain-gauge data. Unsteady pressure fields over the wing were measured using unsteady pressure-sensitive paint (PSP) with temperature-effect correction by temperature-sensitive paint (TSP). Characteristic pressure fluctuations, known as "buffet cells", were observed under the off-design conditions at a bump Strouhal number of 0.2–0.5. The PSP results showed that the buffet cells arise at the mid-span wing at η ≈ 0.45, where a strong shock wave causes an initial boundary-layer separation. Phase shift distributions indicated that a pressure perturbation propagates from the inboard wing toward the outboard wing. The convection velocity and spanwise wavelength were approximately 0.5U∞ and 1.3cMAC, respectively. The angle of attack at which buffet cells first appear was found to be approximately equal to the buffet onset determined by the global criteria, indicating that the occurrence of the buffet cells is deeply related to the buffet onset for the present wing geometry. [ABSTRACT FROM AUTHOR]

There are typographical errors in the original publication of this article. [ABSTRACT FROM AUTHOR]

Transonic buffeting phenomena on a three-dimensional swept wing were experimentally analyzed using a fast-response pressure-sensitive paint (PSP). The experiment was conducted using an 80%-scaled NASA Common Research Model in the Japan Aerospace Exploration Agency (JAXA) 2 m × 2 m Transonic Wind Tunnel at a Mach number of 0.85 and a chord Reynolds number of 1.54 × 106. The angle of attack was varied between 2.82° and 6.52°. The calculation of root-mean-square (RMS) pressure fluctuations and spectral analysis were performed on measured unsteady PSP images to analyze the phenomena under off-design buffet conditions. We found that two types of shock behavior exist. The first is a shock oscillation characterized by the presence of “buffet cells” formed at a bump Strouhal number St of 0.3-0.5, which is observed under all off-design conditions. This phenomenon arises at the mid-span wing and is propagated spanwise from inboard to outboard. The other is a large spatial amplitude shock oscillation characterized by low-frequency broadband components at St < 0.1, which appears at higher angles of attack (α ≥ 6.0°) and behaves more like two-dimensional buffet. The transition between these two shock behaviors correlates well with the rapid increase of the wing-root strain fluctuation RMS. [ABSTRACT FROM AUTHOR]